If you were driving, at 60 mph, and your car got 30 miles per gallon, that would be 2 gallons in one hour, wouldn’t it? Just to ballpark (BIG ballpark) that, at idle, your engine would use 1/2, or 1/3, or 1/4 that. That would be 1 gal, or 2/3 gal, or 1/2 gal. One would need a flow-rate meter, or actually run the engine for a number of hours, starting with a known quantity of fuel.

I believe a very rough estimate is about 1/4 tank over 8 hours. So, assuming your Jeep has a 60 liter tank, you’d use 15 liters per 8 hours, or 1.875 liters per hour. So, 2 liters per hour, I would think would be a decent guess - it works out to 1/2 to 2/3 of a gallon per hour, depending on whether you use US or Imperial gallons.